The present invention relates to the technology to reproduce a processed engine sound in a vehicle interior in response to driving conditions such as an engine speed, a pressing stroke of an accelerator pedal, a vehicle speed, etc.
In recent times the vehicle that emits the smaller engine sound to the vehicle exterior is demanded from the anti-noise viewpoint, still the user makes a request to enjoy a feeling of acceleration or a powerful engine sound in the vehicle interior. For this purpose, various engine sound processing apparatus for catching the engine sound by microphones in the vehicle, then applying a process to this sound, and outputting the processed sound in the vehicle interior have been proposed as the technological section that meets such request. For example, in Patent Literature 1, the system for picking up the engine sound generated in the vehicle, then adjusting the frequency characteristic of this engine sound such that a sound volume in the low-pitched sound is raised in answer to the driving conditions, or the like, and then emitting the processed sound in the vehicle interior has been proposed. Also, in Patent Literature 2, the system for adjusting levels of predetermined degree components of sound waves corresponding to the engine speed in the picked-up engine sound, and then emitting the processed sound in the vehicle interior has been proposed.
[Patent Literature 1] JP-A-2005-134749
[Patent Literature 2] JP-A-2004-74994
Meanwhile, it has been known that a feeling of acceleration that a driver feels from the engine sound depends largely on a spreading feeling of a sound image of the engine sound, i.e., a sound level of a reverberation sound, a reverberation time, etc. Therefore, in order to improve a feeling of acceleration that the driver feels from the engine sound, it is important that an appropriate reverberation sound should be applied to the picked-up engine sound (referred to as a “applying of a reverberation effect” hereinafter). However, it is impossible to apply a reverberation effect in the mode that particular frequency components contained in the engine sound are emphasized, as in the technology disclosed in Patent Literature 1 or 2. Also, it may be considered that the feeling of acceleration should be created by applying a reverberation effect, which has a predetermined reverberation level and a predetermined reverberation time, in the engine sound obtained by the technology disclosed in Patent Literature 1 or 2. In this event, the reverberation effect applied irrespective of the actual driving conditions could cause the driver to feel the feeling of acceleration strange.